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  1. 33 Acta Physica Polonica A

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  1. 26 Kopčanský P.

  2. 23 Timko M.

  3. 13 Závišová V.

  4. 12 Tomašovičová N.

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1
Content available remote

The Dynamics of the Soret Effect in Thin Film of Magnetic Fluid

100%
Kopčanský P., Tomčo L., Timko M., Ocelík V., Koneracká M., Turek I., Štelina J., Musil C.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
875-878
EN
The Soret effect in interference field of two intensive laser beams in the thin film of magnetic fluid was used to create a periodical structure of density of magnetic particles. The structures obtained were indicated using the self-diffraction of the optical beam creating the structures. The relaxation phenomena after switching off the laser interference field were discussed in terms of the spectrum of relaxation times. This spectrum is proportional to hydrodynamic particle size distribution. The relaxation of optical grating consists of two well-defined channels, i.e. decay through single particles and small aggregates, respectively.
2
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Temperature Effect on the Structure of Transformer Oil Based Magnetic Fluids Using Acoustic Spectroscopy

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Kúdelčík J., Bury P., Drga J., Kopčanský P., Závišová V., Timko M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1169-1171
EN
The changes in structural arrangement in transformer oil based magnetic fluids upon the effect of an external magnetic field and temperature were studied by acoustic spectroscopy. The attenuation of acoustic waves was measured as a function of an external magnetic field in the range of 0-300 mT, parallel to the direction of the field and as a function of temperature in the range of 15-35°C for various magnetic nanoparticles concentrations. The strong influence of the steeped magnetic field on the acoustic wave attenuation was detected and its hysteresis was observed, too. When a magnetic field is swept at a constant rate, the dominant interactions between the external magnetic field and the magnetic moment of the nanoparticles occur, leading to the aggregation of magnetic nanoparticles and clusters formation. However, the temperature of magnetic fluids has very important influence on the obtained dependences, where the mechanism of thermal motion acts against the cluster creation. The observed influences of magnetic field and temperature on the investigated magnetic liquids structure are discussed.
3
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Properties of Magnetosome Suspension under the Influence of Magnetic Field

100%
Józefczak A., Molčan M., Rozynek Z., Hornowski T., Skumiel A., Timko M., Tóthová J., Kopčanský P., Leszczyński B.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
629-631
EN
The magnetotactic bacteria synthesize chains of nanosized magnetic particles that function as a compass needle to navigate in the direction of the earth's magnetic field. Magnetosomes are bacterial magnetic nanoparticles containing iron mineral crystals of magnetite or greigite, enveloped by a natural biological membrane. The objective of the work is to study the influence of magnetic field on rheology and acoustic properties of magnetosome suspension. Experimental results show a clear effect of the external magnetic field on the acoustic parameters such as velocity and attenuation of ultrasonic wave, and the viscosity of the suspension, arising from the biogenic magnetic particles aggregation.
4
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Study of Structural Changes of Water-Based Magnetic-Fluid by Acoustic Spectroscopy

100%
Kúdelčík J., Hardoň Š., Bury P., Timko M., Kopčanský P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
919-921
EN
The effect of an external magnetic field on the changes in structural arrangement of magnetic nanoparticles in water based magnetic fluid was studied by acoustic spectroscopy. When a magnetic field is increased, the interaction between the magnetic field and the magnetic moments of nanoparticles leads to the orientation of magnetic nanoparticles and their following aggregation to long chains that cause the increase of acoustic attenuation. The attenuation of acoustic waves measured for jump changes of the magnetic field to 100, 200, and 300 mT at temperature 20°C showed that the changes of acoustic attenuation increased slowly to a stabilized state that after switching off the magnetic field decreased immediately to initial value. The dependence of attenuation of acoustic waves at constant magnetic field on angle between the wave vector and direction of the applied magnetic field (attenuation anisotropy) has been measured, too. The measured anisotropy of acoustic attenuation attested structural changes of magnetic fluid in the magnetic field.
5
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Dielectric Properties of Magnetic Liquids in High Electric Fields

100%
Herchl F., Kopčanský P., Timko M., Koneracká M., Marton K., Kolcunová I., Tomčo L.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
569-572
EN
In this work, dielectric properties of magnetic fluids composed of magnetite particles dispersed in transformer oil and subjected to a uniform magnetic field were investigated at the high alternating electric field intensities in the range of 0.5-2.5 MV/m. Dielectric stability of the magnetic fluid with the particle volume concentrationΦ= 0.0019 was observed. The magnetic fluid with the concentrationΦ= 0.019 showed the significant changes of permittivity and dielectric losses, too.
6
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Structural Phase Transition in Liquid Crystal Doped with Gold Nanoparticles

80%
Kopčanský P., Tomašovičová N., Koneracká M., Timko M., Mitróová Z., Závišová V., Éber N., Fodor-Csorba K., Tóth-Katona T., Vajda A., Jadzyn J., Beaugnon E., Chaud X.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
988-989
EN
The influence of the inclusion of the dodecanethiol functionalized gold particles (with diameter 3-5 nm) on the structural transitions was investigated. The studied samples were based on the nematic liquid crystal 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The volume concentration of the gold particles was ϕ_1 = 2 × 10^{-4} and ϕ_2 = 10^{-3}. The obtained results showed that the inclusion of the gold particles in the 6CHBT liquid crystal increases the sensitivity of such system on the external magnetic field.
7
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Characterization of Fe_3O_4 Magnetic Nanoparticles Modified with Dextran and Investigation of Their Interaction with Protein Amyloid Aggregates

80%
Koneracká M., Antošová A., Závišová V., Lancz G., Gažová Z., Šipošová K., Juríková A., Csach K., Kováč J., Tomašovičová N., Fabián M., Kopčanský P.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
983-985
EN
Functionalised magnetic nanoparticles composed of Fe_3O_4 particles stabilised by sodium oleate and subsequently modified with dextran (MFDEX) were prepared by the co-precipitation method. Their morphology and particle size distribution were observed by scanning electron microscopy and photon cross correlation spectroscopy. In order to confirm the modification of magnetite surface with dextran physical techniques, including infrared spectroscopy, thermal analysis, and magnetic measurement, were used. Finally, the effect of MFDEX on amyloid fibrillar aggregates of human insulin and hen egg white lysozyme, typical amyloidogenic proteins, was investigated. In vitro interaction of MFDEX with protein amyloid fibrils resulted into destruction of amyloid aggregates. The anti-amyloid activity makes MFDEX of potential interest as therapeutic agent against amyloid-related diseases.
8
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Influence of Magnetic Field on Dielectric Breakdown in Transformer Oil Based Ferrofluids

80%
Rajňák M., Dolník B., Marton K., Tomčo L., Molčan M., Kopčanský P., Timko M.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
248-249
EN
In this paper the experimental study of the breakdown field strength in a transformer oil based ferrofluid is reported. The experiments are conducted on five ferrofluid samples with different magnetic volume fraction. The influence of external magnetic field on the breakdown field strength is investigated, when a quasi-homogenous magnetic field was applied in parallel and perpendicular configuration in regard to the electric field. The obtained results are analysed in accordance to the electron charging of ferrofluid nanoparticles theory.
9
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Radiation Stability of the BSA Modified Biocompatible Magnetic Fluid

80%
Tomašovičová N., Haysak I., Kováč J., Kubovčíková M., Závišová V., Timko M., Okunev A., Zorkovská A., Kopčanský P.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
262-263
EN
The aim of the presented work was to investigate the stability of biocompatible magnetic fluid, i.e. water-based magnetic fluid containing magnetite nanoparticles stabilized by surfactant sodium oleate and modified by bovine serum albumin (BSA) after electron irradiation. Samples with the same concentration of Fe_{3}O_{4} but different mass ratio BSA/Fe_{3}O_{4} (w/w=0.25, 1.0 and 2.5) were studied. The electron irradiation caused about 10% reduction of the saturation magnetization in the samples with w/w BSA/Fe_{3}O_{4} ratio of 0.25 and less than 5% in the samples with w/w BSA/Fe_{3}O_{4} ratio of 1 and 2.5.
10
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Magnetic Properties of Ferrofluid with Cobalt Ferrite Particles

80%
Didukh P., Ślawska-Waniewska A., Greneche J., Fannin P.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
587-590
EN
Low temperature Mössbauer investigations of a diluted magnetic fluid containing ultrafine CoFe_{2}O_{4} particles are presented. The thermal evolution of cobalt ferrite particles from the magnetically ordered state to the superparamagnetic state with the blocking temperature at about 80 K, is shown.
11
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Sensitivity of 6CHBT Liquid Crystal Doped with Ferroelectric or Magnetic Particles to Electric and Magnetic Fields

80%
Majorošová J., Tomašovičová N., Timko M., Koneracká M., Studenyak I., Kovalchuk O., Kovalchuk S., Jadżyn J., Kopčanský P.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
260-261
EN
Introduction of ferroelectric or magnetic nanoparticles into nematic liquid crystal is a promising method for the improvement of the electro-optic or magneto-optic properties of different nematic liquid crystals by non-chemical way. This work is devoted to the study of composite systems of liquid crystal with spherical ferroelectric or magnetic particles with the aim to study their sensitivity to electric and magnetic fields. The nematic 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) liquid crystal was doped with SbSI ferroelectric particles or with Fe_{3}O_{4} magnetic particles. The structural transitions in ferronematic samples were indicated by capacitance measurements in a capacitor made of ITO-coated glass electrodes in combined electric and magnetic fields. The obtained results showed the increase of the shift in critical voltage with increasing magnetic field in both kinds of samples.
12
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Magnetization of GaMnN Ceramics Prepared from Nanopowders by an Anaerobic Synthesis and High-Pressure High-Temperature Sintering

80%
Gosk J., Drygaś M., Janik J., Gierlotka S., Pałosz B., Twardowski A.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1a
A-103-A-106
EN
Herein, we report a study on magnetic properties of GaMnN ceramics prepared by no additive high-pressure high-temperature sintering of a range of nanopowders, the latter made via an anaerobic synthesis method in the Ga/Mn bimetallic system at various nitridation temperatures and different levels of initial Mn concentration. Measurements of the magnetization as a function of temperature and magnetic field for the ceramics and parent nanopowders showed a typical paramagnetic behavior. Antiferromagnetic interactions between Mn-ions incorporated in the GaN lattice, GaMnN, were revealed and shown to be much stronger in the ceramics than in the respective nanopowders. In addition, in all of these materials an antiferromagnetic contribution originating from a residual Mn₂SiO₄ by-product was also observed. The highest calculated Mn concentration in the nanopowders reached 3.4 at.%. Complex mixtures of gallium nitride polytypes with multimodal particle size distributions in the nanosized range (small nano: 2-8 nm, large nano: 35-60 nm) were converted upon sintering to the single hexagonal GaN phase with average crystallite sizes of 40-80 nm and higher. For the optimal 700°C-treated materials, the Mn concentration in the parent GaMnN nanopowder was 3.2 at.% whereas in the derived ceramics it amounted to 5.5 at.%. At the same time, contributions of the adventitious Mn₂SiO₄ by-product significantly decreased upon sintering.
13
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Viscosity Dependence of a Magnetic Fluid Nanoparticles Concentration

80%
Tóthová J., Kováč J., Kopčanský P., Rajňák M., Paulovičová K., Timko M., Józefczak A.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
278-279
EN
In this work we have studied the effect of temperature on the viscosity of magnetic fluids (MFs) based on the transformer oil ITO 100. The volume concentration of suspended magnetic particles (MPs) changed from 0.25 to 1%. Rheological characterization of MFs was performed using a vibroviscometer at working frequency of 30 Hz. The temperature dependence of the viscosity was measured in the temperature range from 20 up to 50 °C. The magnetization of different concentrations of MPs in MFs was determined by using the vibrating sample magnetometer.
14
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[FeCl_{4}]¯ Ionic Liquid Based Ferrofluids

80%
Parnica J., Kesa P., Kovac J., Timko M., Antalik M.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
276-277
EN
Magnetic ionic liquids derived from hydrochloride methyl ester alanine amino acids (AA) and FeCl_{3} were synthesized in ethanol and their magnetic properties were investigated. Iron (III) chloride forms ionic liquid in ethanol at saturated concentrations by the transfer of Cl¯ anion from one molecule of FeCl_{3} to the other molecule with the creation of tetrachloro ferrate anion [FeCl_{4}]¯ as well as dimer [Fe_{2}Cl_{7}]¯. Raman scattering indicates that after addition of hydrochloride methyl ester alanine to ethanol solutions of FeCl_{3} increase the intensities of signal at the frequencies at 318 cm^{-1} and 380 cm^{-1} as markers for the presence of [FeCl_{4}]¯ and [Fe_{2}Cl_{7}]¯ complexes. The magnetization at room temperature showed in both samples a linear dependence on the applied magnetic field. On the other hand, in the Raman scattering experiments the magnetization is smaller for FeCl_{3} sample in the presence of methyl ester alanine.
15
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Dielectric Properties of Lyotropic Magnetic Liquid Crystal

80%
Kopčanský P., Tomčo L., Jadzyn J., Swiergiel J., Majorošová J., Kubovčíková M., Timko M., Rajňák M., Šipošová K., Gažová Z., Bednariková Z., Hu C.-K., Hayryan S., Studenyak I., Kovalchuk T., Kovalchuk O.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
632-634
EN
An important feature of lyotropic liquid crystals is the self-assembly of the amphiphilic molecules as supermolecular structures. We have studied the formation of nematic liquid crystal phase in solutions containing lysozyme amyloid fibrils and magnetic nanoparticles using oscilloscopic method. Interaction of fibrils with magnetic nanoparticles under the external magnetic field resulted in fibril re-arrangement. The analysis of the obtained results suggests that the decrease in conductivity of solutions in presence of magnetic field is due to decrease of the ion mobility caused by re-arrangement of structures in the solution. The obtained results allow determination of the optimum ratio of the components which can lead to preparation of solutions with a more ordered structure in presence of magnetic field.
16
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How to Enhance Sensitivity of Liquid Crystals to External Magnetic Field?

80%
Kopčanský P., Tomašovičová N., Gdovinová V., Timko M., Éber N., Tóth-Katona T., Jadzyn J., Honkonen J., Chaud X.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
157-162
EN
Liquid crystals, due to their large dielectric anisotropy, respond very sensitively to application of an external electric field, whereas they are only weakly sensitive to the magnetic field. A possible way of improving that sensitivity is doping liquid crystals with magnetic nanoparticles. As a result, stable colloidal suspensions of liquid crystals with relatively low concentrations of magnetic nanoparticles (called ferronematics, ferrocholesterics, ferrosmectics, etc.) can be produced. We illustrate some examples of the influence of the magnetic field, as well as of a superposition of magnetic and electric fields on the structural transitions (e.g. on the Fréedericksz transition) in ferronematics based on the calamitic liquid crystal 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). It is shown that the samples respond to the applied magnetic field of low strength. The effects of the magnetic particles and magnetic field on the nematic to isotropic phase transition temperature are discussed as well.
17
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Low Magnetic Field Response in Ferronematics

80%
Gdovinová V., Tomašovičová N., Závišová V., Éber N., Tóth-Katona T., Royer F., Jamon D., Jadzyn J., Kopčanský P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
934-936
EN
In this work the 4-n-hexyl-4'-cyanobiphenyl liquid crystal was doped with differently shaped magnetite nanoparticles. The structural changes were observed by capacitance measurements. Influence of the shape of magnetic particles on magnetic Fréedericksz transition depends on the type of anchoring, which is characterized by the density of the anchoring energy and by the initial orientation between the liquid crystal molecules and the magnetic moment of the magnetic particles. It was observed that in the case of doping with spherical particles, the critical magnetic field is shifted to higher values with increase of volume concentration of the magnetic nanoparticles but decreases with increase of biasing voltage. In the case of doping with rod-like particles, the critical magnetic field is almost independent of the volume concentration of the magnetic nanoparticles.
18
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The Influence of Magnetic Particles on the Nematic Droplets Formation in Liquid Crystal

80%
Majorošová J., Gdovinová V., Tomašovičová N., Juríková A., Závišová V., Jadzyn J., Kopčanský P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
955-957
EN
In this work the thermotropic nematic liquid crystal 4-trans-4'-n-hexyl-cyclohexyl-isothiocyanato-benzene (6CHBT) was dissolved in phenyl-isothiocyanate and doped with spherical magnetic particles with volume concentration ϕ₁=10¯⁴ and ϕ₂=10¯³. The influence of the volume concentration on the phase transitions from isotropic to nematic phase was studied by three experimental methods: optical microscopy, differential scanning calorimetry, and dielectric measurements. The obtained results confirmed the coexistence of isotropic and nematic phase, i.e. nematic or ferronematic droplets in isotropic phase in a wide temperature range between nematic and isotropic phase.
19
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The Structural Phase Transitions in 6CB-Based Ferronematics

80%
Tomašovičová N., Koneracká M., Kopčanský P., Timko M., Závišová V., Tomčo L., Jadżyn J.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
336-338
EN
The structural transitions in ferronematics based on the thermotropic nematic liquid crystal 4-cyano-4'-hexylbiphenyl were studied. The ferronematic samples were prepared by doping with magnetic suspension consisting of Fe_3O_4 particles (10 nm in diameter) coated with oleic acid as a surfactant with different volume concentrations of magnetic particles (from 10^{-5} to 10^{-3}). Freedericksz transitions were studied in combined electric and magnetic fields. The experimental results indicated soft anchoring with perpendicular initial orientation between the magnetic moment of the magnetic particles and director.
20
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The Anchoring Energy of Liquid Crystal Molecules to Magnetic Particles in HAB-Based Ferronematics

80%
Tomašovičová N., Koneracká M., Kopčanský P., Timko M., Závišová V., Vajda A., Fodor-Csorba K., Éber N., Tóth-Katona T., Jadzyn J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
591-594
EN
In this work we describe the magnetic Freedericksz transition in HAB-based (4, 4'-di-n-heptylazoxybenzene) ferronematics. The ferronematic samples were prepared with two different volume concentrations of magnetic particles φ_1 = 2×10^{-5} and φ_2 = 2×10^{-4}. The liquid crystal HAB is nematic at the temperatures from ≈53°C to 70°C and smectic A at the temperatures under 53°C. The anisotropy of dielectric permitivity of HAB liquid crystal is positive in nematic phase and negative in smectic A phase. The magnetic Fredericksz transition was studied in nematic phase at temperature 60°C.
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